Method of distillation of phenolic compounds



y 1941- M. J.,P. QB OGAR T ETAL 2,241,110

METHOD'OF DISTILLATION OF PHENOLIC COMPOUNDS Filed Nov. 8, 1938 2 Sheets-Sheet 1 Vacuum Steam INVEN 0R5 Mme; .fifiogart and Bottoms produot ATTORNEY May 6, 19411 M. J. P. BOGART EIAL METHOD OF DISTILLATION 0F PHENOL IC COMPOUNDS 2 Sheets-Sheet 2 Filed NOV. 8, 1938 Overhead Product Feed Bottom Product INVENTORS MarcelJEbqgartand BY games 3.5 6

v A ATTORNEY ter Patented May 6, 1941 UNITED STAT Es PATENT oFFicE METHOD or nIsmm'noN 0F rnENomo COMPOUNDS Marcel r. r. Bogart, Teaneck, and James s. F.

Carter, Passaic, N. 1., assignors to The Lummus Company, New York,

Delaware N. Y., a corporation 01' Application November s, 1938. Serial No. 239,452

1 Claim.

tend. to converge under increasing pressures, has

been difficult due to the fact that a lar e number of bubble decks is required and the pressure drop requires a pressure approaching or equal to a critical point at which separation is impossible. Furthermore, the pressure limits of a large number of decks require an excessively high "temperature heating medium for the high pressures and arr-extremely low temperature for the low pressures which has added to the operating diflicultios Some mixtures have thus proved commercially inseparable.

One of the principal objects of this invention is to provide an improved method by which the separation of close boiling point products is made Further objects and advantages of our invention will appear from the following description of a preferred form of embodiment thereof taken in connection with the attached drawings, in which: a

Figure l is a diagrammatic layout of a single two-part column in accordance with our invention; and

I Figure 2 is a diagrammatic layout of a plurality of single step columns as a modnfled form V of embodiment of the invention.

I In accordance with a preferred form of embodiment of our invention, we have shown a distilling column having a primary distillation section l0, and a" secondary distillation section I! which may be mounted on top of the primary distillation section III, but which is entirely seppossibieand by which a more accurate control can be had and operating costs materially relatively close boiling point materials in which a complete separation of one end product is obtained in a primary distillation step and a complete separation of another end product is obtained in a subsequent distillation step with the overhead from the first distillation step condensed so that there is a minimum difference in pressures between the respective ends of the distillation zones.

Another object of the invention is to provide an improved method of distilling close boiling point materials in which the distillation takes place in a plurality of steps with the bottoms product of the subsequent step used as reflux for the initialstep and with the bottoms prodnot of the first step and the overhead product of the subsequent step constituting the end products.

A still further object of the invention is to provide an improved distillation apparatus having a large number of individual decks so interconnected as to provide a relatively low maximum, pressure drop between the top and the bottom of the distillation zones. The problems surrounding the separation of ortho from para chlortoluene are described and claimed in our co-pending application Serial No. 201,864, April 14, 1938.

arated therefrom as by the closed plate section I4. The feed, which is a mixture of products.

having relatively close boiling points, is preferably introduced at I8 or at any other point in the two distillation zones. It is most satisfactory, however, when introduced into that part of the distillation zone having materials most nearly approaching the relative proportion of the mixed materials. Heat may be provided by the steam circuit l8, conveniently mounted in the bottom of the primary distillation section. The bottoms product is removed at 20.

The overhead in the primary distillation section i0, is removed through the vapor pipe 22 and completely condensed by the condenser 23. The liquid condensate is fully separated in the separator 24 on which a vacuum is maintained by the vacuum line 25. The condensate is. then drawn oil at and passed through the heat exchanger 21 and vaporized. The vapor is introduced into the bottom of the secondary distillation zone l2 through the vapor line 28.

The secondary distillation ,step of this condensate removed overhead from the first distillation is carried out in the secondary distillation zone I2 with the overhead removed at 30 and passed through condenser it. This is also operated under vacuum obtained by the vacuum line 33 operating on the separator 34. Reflux is returned at 36 to the top of the secondary distilling section l2, and the overhead product is removed at 3'1. The bottoms are passed into the first distillation zone In through pipe 38 and this serves as reflux.

It will be seen that the mixture is thus given a. two-step separation in the respective distillation sections. The maximum differences in pres- 55 .sure between the top and bottom of the respective distillation sections due to pressure drop throughthe multiplicity of decks is not; great, however, as each section is subjected to a vacuum which is possible by the condensation of the overhead vapors in each section. It is possible, under such circumstances, to obtain a complete separation of the bottoms product at as a result of the first distillation and a complete and pure overhead product can be produced at 5i? as the overhead from the secondary distillation.

This is of especial advantage 'where the boiling points of the mixed products are relatively close together and where the vapor pressure curves tend to converge at the high pressures. As is well known, mixtures of cresol and phenol or mixtures of ortho-cresol and meta-cresol, as well as many other mixtures of similar type best be efiectively separated only at relatively low absolute pressures and such separation is or dinarily so incomplete, that it. has been considered commercially unsatisfactory. With the apparatus as described, the pressure drop in each distillation zone can be kept at a minimum with I the resulting substantially lower total pressure drop. As a specific example, it is possible to revduce the usual required pressure range of 50 mm.

to 330 mm. when one hundred and forty decks of the usual 2 mm. pressure drop are used to a range of 50 mm. to 190 mm. in each section of seventy decks. Not only does this improved pressure range make separation of difilcultly separable mixtures commercially practicable, but

economies in operation are possible with a' smaller temperature range possible'by the dependent distillation sections.

If it should be found desirable to subdivide the column, it is of course entirely practical to do .so. An arrangement which shows such a construction is illustrated in Figure 2. The primary column @015 adapted to receive feed at M of a mixture of closely boiling materials as in the first case, and such materials are initially dis tilled within this column. Heat is conveniently supplied by the steam line 52 in heat exchange relation in heat exchanger 43 with a bottoms rebelling circuit 46 and with the steam under automatic control 85.

A part of the bottoms material is collected at at in a bottoms chamber having a vacuum vent ll. The liquid level in the bottom of the primary distillation column 40 is under control of the liquid level control 48 which operates the valve 59 on the bottoms product discharge line. The remainder of the bottoms material is recircu lated at it-for heating as above described.

The overhead vapors from the primary column are discharged at 5! into the total condenser 52,

the temperature of which is maintained uniform by the incoming cooling medium lid, under temperature control operated from the condensate line 56. The condensate from the condenser 52 is separated from the uncondensable gas in the liquid separator 51 which is under vacuum from the line 58. A vent cooler 59 may be placed in this line to assure the complete separation of liquid from the gases.

aasiuio The condensate removed at 56 is again distilled for the complete removal of the second end product. This is accomplished by heating the condensate in the heat exchanger 60 and introducing vapors into the secondary distillation column 64. The vapors may be introduced at B5 or 66 depending on whether or not some separation is desired between the feed and the bottoms material. As in the prior case, the heating of the feed is conveniently accomplished by passing the V condensate through a heat exchanger 60 which is efiectively heated bysteam introduced at 6| and under control of pressure control valve 62. The bottoms product removed at I8 may be in part circulated through the heat exchanger 60 under suitable control of valve 84.

In this second distillation column, the vapors which are removed overhead at 58, are condensed at 89 by a cooling medium 10 and the liquid is separated from the uncondensable gases in the separator H which is under a vacuum from the line 58. A vent cooler 12 may also be placed in the vacuum line. The liquid removed through the line H becomes the final overhead end product which is conveniently collected at 15 in a suitable chamber having the vacuum vent I6.

A part of the bottoms from the second column 64, removed at 18, is conveniently pumped by the pump 19 as reflux through the line to the top of the first column 40. If desired, an automatic liquid level control valve 82 may be provided in this line. It is to be understood, however, that the reflux need not be continuously withdrawn from the second column for return to the first, but that reflux liquid may be collected from any desired source and returned as needed. Similarly, the operation of the second column need not be precisely dependent on the first column as the intermediate liquid mixture removed at 56 may be accumulated and introduced as desired to the second column. There are den.-

nite advantages, however, in having a continubodiment of the invention, we are aware that tend to converge at higher pressures, into separate products of a purity obtainable only at absolute pressures beyond the range of conventional apparatus which comprises the steps of continuously feeding the mixtureto a multi-stage distillation system having bubble decks, the gross pressure drop across which if applied to all the decks would be in excess of the allowable pressure drop for the desired purity of end products, said feed being to a point in the system in which there is substantial similarity of composition, applying a vacuum to one stage and continuously removing an overhead therefrom, the total pressure drop in said stage being insufiicient to interfere with the production of a pure end product. removing the bottoms of said first stage and feeding said bottoms to an upper portion of a second stage as a feed and in liquid form as reflux to form full yield of bottoms product, applying avacuum to said second stage, the pressure drop in such stage being insufficient to interfere with the production of a second pure product in the bottoms thereof, condensing and revaporizing the overhead from said second stage, and feeding said vapors to the first stage to form a full yield of overhead end product, said vapors consisting primarily of the overheadend product,

thebottoms of said first stage being primarily constituents of the bottoms end products. 

